I've come here to show you how to make the origami flip toy (Ddakji) that Gi-hun and the train-station guy play with.
Colored paper
Get a 3:2 sheet of paper and crease it along the lies as shown below. I have use a 21x14 cm sheet. So the Ddakji I'll have in the end will be 7x7 square.
Fold it in half.
Make diagonal folds as shown in the figure above. You will need two such shapes so repeat the steps 1, 2, and 3 with another 3:2 sheet of paper.
Place the two shapes you made as shown below.
Next, fold the top flap onto itself.
Then fold the left flap over it.
After that, fold the bottom flap over them both.
Finally, slip the pointed edge of the remaining flap into the little pocket indicated by the arrowhead.